DESCRIPTION: This revised application describes experiments designed to clarify therole of a protein produced by E. corrodens which has been implicated as a toxin with effects on human epithelial cells, fibroblasts, and HL60 cells.A monoclonal antibody has been identified which blocks the toxic activities of the organism, and that Mab reacts with an approximately 72Kd molecule produced by E. corrodens. Interestingly, the Mab also cross-reacts with a protein of apparently 140Kd produced by S. sanguis. Antisera reactive to the 140Kd protein also react with the E. corrodens 72Kd molecule. The experimental plan described in this application is to clone and inactivate the gene encoding the 72Kd molecule from E. corrodens and evaluate the effects of its inactivation on the toxicity in various cell culture systems.